The use of alkoxylated non-ionic as surface active agents is well known. The ethoxylation of fatty alcohols results in compounds that have both water soluble and oil soluble groups. The result is a so called “surfactant”, a contraction for surface active agent. The addition of ethylene oxide to fatty alcohol results in increasing water solubility.
The term “HLB” was first employed by the lab staff of the Atlas Powder Co. in America. This means the balance between the oil soluble and water soluble moieties in a surface active molecule, and is expressed as the “Hydrophile—Liphophile Balance”. A more oil-soluble emulsifier shows a lower HLB and a more water-soluble emulsifier shows the reverse. HLB is a very useful method in selecting an emulsifier, but it still has several limitations to application for every surfactant.
The HLB system developed by Griffin some 50 years ago. The system depends upon the observation that the solubility of the surfactant is related to the percentage by weight of polyoxyalkylene portion of the molecule and is relatively independent of the nature of the fatty group.
Water DispersibilityHLB% EO.Not dispersible1-4up to 20%Poorly dispersible4-620%-30%Milky dispersion6-830%-40%Stable milky dispersion 8-1040%-50%Translucent to clear10-1350%-65%Clear Solution13+Over 65%
HLBApplication.4-6W/O Emulsifier7-9Wetting Agent 8-18O/W Emulsifier13-15Detergents15-18Solubilizers
The HLB system has some very distinct situations I which the applicability breaks down. It is designed for ethoxylated products, specifically linear alcohol ethoxylates. It is not useful when applied to Guerbet alcohol ethoxylates due to the branching. We have also surprisingly and unrepentantly found that certain ester that are linked together through a linking group are not surfactants, despite high levels of ethoxylates. We have dubbed these spider esters since the structure is reminiscent of a spider. The crosslinking group is the body of the spider and the ethoxylated fatty esters are the legs. A specific order is also needed. The ethoxylated needs to be closest to the body of the spider and the fatty group at the foot end. While not wanting to be limited by any one theory we believe this orientation limits rotation of the polyoxyalkylene group and causes the molecule to be incapable of orientation at the surface of a water oil interface. Such orientation results in water solubility caused by the polyoxyalkylene groups going into the water and the oil soluble group going into the oil phase. The result is an ester that contains an appreciable amount of polar polyoxyalkylene group but is water insoluble. This is a very interesting material in that it represents a polar rich oil in which polar and ionic materials may be dissolved and applied in an oil phase. This is a critical concept for delivery of antioxidants, free radical scavengers, sun screens and the like to the skin.
Surfactants are by definition compounds that remove natural oils from the skin. The removal of oil from the skin is a stripping process that damages the skin and provides dry chapped skin. Surfactants in the process of emulsification, detergency or wetting have a cleaning effect in removing soil from the skin, but concurrently cause dry skin. This process results in dry skin and cosmetically unacceptable appearance to the skin. Dry skin is a major consumer problem in the cosmetic industry.
It is generally accepted that there are different mechanisms of providing emolliency to the skin. The first is to provide moisture in so called moisturizing compounds. These compounds allow moisture to penetrate the skin. The alternate method is to trap moisture inside the skin providing a barrier that does not allow moisture to be lost. The barrier is a water insoluble oil that when placed on the skin keeps moisture from evaporating. It is clear that the two different mechanisms are mutually exclusive. That is, if an emollient oil is applied to the skin, not only can moisture not exit the skin, but moisture cannot enter, traversing the barrier. If a moisturizer is applied to the skin it must be applied to a barrier free skin. Simply put you cannot have effective moisturization on skin with a barrier present, since it will not penetrate. There is a long felt need for a technology that provides moisturization and emolliency. This requires a non-surface active polar oil that can simultaneously have water binding sites and oil soluble sites. Such a combination of properties has been elusive until the process of the current invention was discovered.
We have unexpectedly and surprisingly found that molecules of the present invention, by virtue of having the polyoxyalkylene group bonded on one side to a fatty group and on the other to a common backbone, compounds that have polyoxyalkylene contents that would render them water soluble if they were present in non-spider esters. These polar esters link a fatty group through a polyoxyalkylene group to a common polymeric backbone. While not wanting to be held to one specific theory, the functionality of the present molecules has to do with the balance between the fatty group and the water soluble group and requires limitation on the orientation of the resulting polymer. The result is an ester that has little or no water solubility, an ability to deliver water and no surface activity.
By polyoxyalkylene groups is meant polyethylene groups —(—(CH2CH2O)aH), polyoxypropylene groups (—CH2CH(CH3)O)bH) or mixtures thereof (—(CH2CH2O)a—CH2CH(CH3)O)bH).